Questions remain about the historic success or failure of ground-breaking investment to retrofit a ferry to burn methanol as a fuel six years ago.

In 2015, Swedish ferry giant committed to a $22m retrofit of the 1,300-passenger ferry Stena Stena Germanica (built 2001) to enable it to burn the lower carbon fuel.

However, with the regulatory landscape still not fixed, it remains unclear whether it is a ground-breaking model or a blind alley, one of the company’s senior executives has admitted.